Question

我在尝试将不同的JavaScript字符串操作解决方案应用于我的特定问题时遇到了麻烦：

string str = ":2 E/4 :2 G/4 |:2 G/4 :2 F/4"

从字符串的末尾开始，我想一直删除到找到的第一个:。

1次删除：

":2 E/4 :2 G/4 |:2 G/4 "

2次移除：

":2 E/4 :2 G/4 |"

3次移除：

":2 E/4 "

我该怎么做？

Answer 1

使用String.split，Array.slice和Array.join函数的解决方案：

/**
 * @param string str Input string with 'colons'
 * @param number removals Number of removals
 * @returns string
 */
var sliceToColon = function (str, removals) {
    var parts = str.split(":");
    return parts.slice(0, -removals).join(":");
}

console.log(sliceToColon(":2 E/4 :2 G/4 |:2 G/4 :2 F/4", 1)); // :2 E/4 :2 G/4 |:2 G/4 
console.log(sliceToColon(":2 E/4 :2 G/4 |:2 G/4 :2 F/4", 2)); // :2 E/4 :2 G/4 |
console.log(sliceToColon(":2 E/4 :2 G/4 |:2 G/4 :2 F/4", 3)); // :2 E/4

Answer 2

您可以使用lastindexof()获取":"的最后一次出现，然后使用substring()

提取该索引位置之前的所有字符

var str = ":2 E/4 :2 G/4 |:2 G/4 :2 F/4";
var n = str.lastIndexOf(":");
console.log(str.substring(0, n));

Answer 3

试试这个。

<!DOCTYPE html>
<html>
<body>

<button onclick="myFunction(':2 E/4 :2 G/4 |:2 G/4 :2 F/4','2')">Click</button>
<script>
function myFunction(str,n) {
var x,y;
for (i = 0; i < n; i++) {     
    x=str.lastIndexOf(":");
    y=str.substr(0,str.lastIndexOf(":"));
str= y;
}
document.getElementById("demo").innerHTML =  y;
}
</script>

</body>
</html>

Answer 4

一个选项，虽然比许多选项稍微冗长，但是如下：

function removeLastNSections(opts) {

  // the default settings,
  // text:       String, must be user-supplied;
  //             the string to be split and from
  //             which 'sections' should be removed.
  // separator:  String,the character upon which
  //             string should be split.
  // n:          Number, or numeric String (4 or '4'),
  //             the number of 'sections' to remove.
  var settings = {
    'text' : null,
    'separator' : ':',
    'n' : 1
  },
  haystack,
  numSections;

  // updating the defaults with user-supplied values:
  Object.keys(opts || {}).forEach(function(key){
    settings[key] = opts[key];
  });

  // if settings.text exists:
  if (settings.text) {

    // we split the user-supplied string of text on
    // occurrences of the separator:
    haystack = settings.text.split( settings.separator );

    // an integer for the length of the haystack array:
    numSections = haystack.length;

    // we slice the haystack array, taking all elements from
    // the first (index: 0) to the index resulting from the
    // sum of the number of elements in the array minus the
    // number of 'sections' to remove:        
    return haystack.slice(0, numSections - settings.n )
      // and join those array-elements back into a
      // a string by joining them together with the
      // separator:
      .join( settings.separator );
  }

  return '';
}
console.log(
  removeLastNSections({
    'text' : ":2 E/4 :2 G/4 |:2 G/4 :2 F/4"
  })
); // => :2 E/4 :2 G/4 |:2 G/4 
console.log(
  removeLastNSections({
    'text' : ":2 E/4 :2 G/4 |:2 G/4 :2 F/4",
    'n': 1
  })
); // => :2 E/4 :2 G/4 |:2 G/4 
console.log(
  removeLastNSections({
    'text' : ":2 E/4 :2 G/4 |:2 G/4 :2 F/4",
    'n' : 2
  })
); // => :2 E/4 :2 G/4 |
console.log(
  removeLastNSections({
    'text' : ":2 E/4 :2 G/4 |:2 G/4 :2 F/4",
    'n' : 3
  })
); // => :2 E/4

function removeLastNSections(opts) {
  var settings = {
      'text': null,
      'separator': ':',
      'n': 1
    },
    haystack,
    numSections;

  Object.keys(opts || {}).forEach(function(key) {
    settings[key] = opts[key];
  });

  if (settings.text) {
    haystack = settings.text.split(settings.separator);
    numSections = haystack.length;

    return haystack.slice(0, numSections - settings.n).join(settings.separator);
  }

  return '';
}
console.log(
  removeLastNSections({
    'text': ":2 E/4 :2 G/4 |:2 G/4 :2 F/4"
  })
);
console.log(
  removeLastNSections({
    'text': ":2 E/4 :2 G/4 |:2 G/4 :2 F/4",
    'n': 1
  })
);
console.log(
  removeLastNSections({
    'text': ":2 E/4 :2 G/4 |:2 G/4 :2 F/4",
    'n': 2
  })
);
console.log(
  removeLastNSections({
    'text': ":2 E/4 :2 G/4 |:2 G/4 :2 F/4",
    'n': 3
  })
);

参考文献：

使用JavaScript从字符串末尾开始的字符串操作

4 个答案: